1. Field of the Invention
The present invention relates to a color video signal reproducing apparatus and, in particular, relates to one for locking a color frame with a control signal (CTL signal) recorded on a tape.
2. Description of the Prior Art
In a helical type video tape recorder (hereinafter simply named a VTR), by using a tracking technique where rotating magnetic heads follow a track formed on a magnetic tape, even when a signal is reproduced in a different speed reproduction mode where the magnetic tape is traveled at a different speed from that at which it was recorded, an image with a high quality can be obtained. The capstan motor is controlled so that the tracking reproduces a CTL signal which is recorded in the longitudinal direction of the magnetic tape and the phase of the reproduced CTL signal matches a servo reference.
In a broadcasting station, the start position of a news material, a commercial message (CM) material and the like is checked previously by reproducing it in the still reproduction mode of a VTR. At a desired time, the VTR is switched to constant speed reproduction mode and then the news material, commercial material and the like is broadcast. In this case, when the signal is switched, a color frame of a reproduced color video signal of the VTR should be immediately synchronized with that of a reference color video signal of the broadcasting station so as to keep color subcarriers and sync signals continuous.
In the above mentioned method where the CTL signal is detected and then servo-locked, the magnetic tape is started up from the stop state to the normal (.times.1) speed traveling state. In addition, the phase of the CTL signal reproduced from the magnetic tape is matched with that of the reference color video signal. In order to perform this operation quickly, it is necessary to drive the magnetic tape with a maximum acceleration and control the system so that the phase of the CTL signal which was just reproduced matches that of the reference color video signal when the speed of the magnetic tape becomes the normal (.times.1) speed.
As this type of technique, when the particular speed is obtained after the traveling speed of the magnetic tape is constantly accelerated both the phases are matched in phase comparison mode. For example, a prior art system according to this type of technique is officially disclosed as Japanese Patent Laid-open No. SHO 61-290893. This prior art is such that a capstan motor, a magnetic tape, and so forth are stopped in the still reproduction mode and a color frame at this time is written to memory. Thereafter, when the still reproduction mode is switched to the constant speed reproduction mode, the capstan motor is started and rotates at a high speed and thereby the magnetic tape is rapidly moved. When a start command signal is sent, the color frame of the reference color video signal is compared with that of the reproduced color video signal which is read from the memory and at which the magnetic tape was stopped. When an ID signal of the reproduced color video signal is detected in a particular period of time equally spaced from that of the reference color video signal, it is determined that both the color frames are matched and thereby 2n frames are phase matched. On the other hand, when the ID signal of the reproduced color video signal is not detected in the above mentioned period of time, it is determined that both the color frames are not matched and thereby (2n+1) frames are phase matched. In this manner, the phase of the reference color video signal can be matched with that of the reproduced color video signal.
However, according to the above mentioned prior art, a particular number of frames should be phase matched so as to match the phase of the reference color video signal and that of the reproduced color video signal.
To solve such a problem, a technique known as the so-called stop control has been developed. In this technique, the phase of the CTL signal is read until the magnetic tape is stopped. The magnetic tape is stopped at an optimum phase (namely, so that the phase of the reproduced CTL signal is matched with that of the reference color video signal when the magnetic tape with the maximum acceleration applied is driven at the normal (.times.1) speed). Thereafter, the magnetic tape is started from such a phase.
With this technique, the phase matching operation is not necessary. However, the probability where the phases of the color frames are matched in the NTSC scheme is 50% because one color frame is composed of two frames; and that in the PAL scheme is 25% because one color frame is composed of four frames. When the phases of the color frames are not matched and the color frames are locked, the lock up time becomes disadvantageously long.